Range queries for scoring in Redis

Introduction

Range queries let you find items with scores between two values. This helps when you want to filter or sort data by numbers like points or prices.

Finding all players with scores between 50 and 100 in a game leaderboard.

Getting products priced between $10 and $50 in an online store.

Listing events happening between two dates stored as timestamps.

Filtering movies with ratings between 7 and 9 stars.

Syntax

Redis

ZRANGEBYSCORE key min max [WITHSCORES] [LIMIT offset count]

min and max define the score range. Use -inf or +inf for open ranges.

Adding WITHSCORES returns the scores along with the items.

Examples

Get all members with scores from 50 to 100.

Redis

ZRANGEBYSCORE leaderboard 50 100

Get products priced between 10 and 50, showing their prices.

Redis

ZRANGEBYSCORE products 10 50 WITHSCORES

Get first 5 events with scores up to 1609459200 (a timestamp).

Redis

ZRANGEBYSCORE events -inf 1609459200 LIMIT 0 5

Sample Program

This adds four players with scores, then finds those scoring between 50 and 100, showing their scores.

Redis

ZADD leaderboard 30 "Alice" 70 "Bob" 90 "Carol" 110 "Dave"
ZRANGEBYSCORE leaderboard 50 100 WITHSCORES

Important Notes

Scores are numbers used to sort members in sorted sets.

Use -inf and +inf to represent negative and positive infinity for open-ended ranges.

LIMIT helps paginate results when you have many matches.

Summary

Range queries filter sorted set members by score.

Use ZRANGEBYSCORE with min and max to specify the range.

WITHSCORES option shows scores alongside members.

Practice

1. What does the Redis command ZRANGEBYSCORE do?

easy

A. It returns members in a sorted set within a specified score range.

B. It deletes members from a sorted set based on score.

C. It adds new members to a sorted set with scores.

D. It returns the total number of members in a sorted set.

Solution

1. Step 1: Understand the command purpose

   ZRANGEBYSCORE is used to get members from a sorted set filtered by score range.

2. Step 2: Compare options with command behavior

   Only "It returns members in a sorted set within a specified score range." correctly describes returning members within a score range.

3. Final Answer:

   It returns members in a sorted set within a specified score range. -> Option A

4. Quick Check:

   ZRANGEBYSCORE = returns members by score range [OK]

Hint: ZRANGEBYSCORE fetches members filtered by score range [OK]

Common Mistakes:

• Confusing ZRANGEBYSCORE with commands that add or delete members
• Thinking it returns count instead of members
• Assuming it sorts members by name instead of score

2. Which of the following is the correct syntax to get members with scores between 10 and 20 from a sorted set named myzset?

easy

A. ZRANGEBYSCORE myzset [10 [20

B. ZRANGEBYSCORE myzset (10 (20

C. ZRANGEBYSCORE myzset 10 20

D. ZRANGEBYSCORE myzset "10" "20"

Solution

1. Step 1: Recall basic syntax of ZRANGEBYSCORE

   The command format is ZRANGEBYSCORE key min max where min and max are numbers or special strings.

2. Step 2: Analyze options for correct syntax

   ZRANGEBYSCORE myzset 10 20 uses plain numbers 10 and 20 correctly. Options A and B use parentheses or brackets which mean exclusive or inclusive but are not needed here. ZRANGEBYSCORE myzset "10" "20" uses quotes which are unnecessary.

3. Final Answer:

   ZRANGEBYSCORE myzset 10 20 -> Option C

4. Quick Check:

   Syntax = ZRANGEBYSCORE key min max [OK]

Hint: Use plain numbers for inclusive score range in ZRANGEBYSCORE [OK]

Common Mistakes:

• Using parentheses or brackets incorrectly for inclusive ranges
• Adding quotes around numeric scores
• Mixing up min and max order

3. Given the sorted set myzset with members and scores: {"a":5, "b":10, "c":15, "d":20}, what is the result of ZRANGEBYSCORE myzset 10 20 WITHSCORES?

medium

A. ["b", "10", "c", "15", "d", "20"]

B. ["a", "5", "b", "10", "c", "15"]

C. ["c", "15", "d", "20"]

D. ["a", "5", "d", "20"]

Solution

1. Step 1: Identify members with scores between 10 and 20 inclusive

   Members with scores 10, 15, and 20 are "b", "c", and "d" respectively.

2. Step 2: Understand WITHSCORES option output

   WITHSCORES returns members and their scores as alternating elements in the list.

3. Final Answer:

   ["b", "10", "c", "15", "d", "20"] -> Option A

4. Quick Check:

   Members with scores 10-20 + WITHSCORES = ["b", "10", "c", "15", "d", "20"] [OK]

Hint: WITHSCORES returns member-score pairs in order [OK]

Common Mistakes:

• Including members outside the score range
• Returning only members without scores
• Mixing order of members and scores

4. What is wrong with this command to get members with scores between 5 and 15 from myzset?

ZRANGEBYSCORE myzset 5 15 WITHSCORE

medium

A. The score range should be reversed as 15 5.

B. The option should be WITHSCORES, not WITHSCORE.

C. The command needs a LIMIT clause to work.

D. The key name must be quoted.

Solution

1. Step 1: Check the option spelling

   The correct option to include scores is WITHSCORES (plural), not WITHSCORE.

2. Step 2: Verify other parts of the command

   The score range 5 to 15 is correct, LIMIT is optional, and key names do not require quotes.

3. Final Answer:

   The option should be WITHSCORES, not WITHSCORE. -> Option B

4. Quick Check:

   Correct option spelling = WITHSCORES [OK]

Hint: Use WITHSCORES (plural) to get scores with members [OK]

Common Mistakes:

• Misspelling WITHSCORES option
• Reversing min and max scores
• Adding unnecessary quotes around key

5. You have a sorted set players with player names and their scores. You want to find all players with scores greater than 50 but less than or equal to 100, including their scores. Which command correctly achieves this?

hard

A. ZRANGEBYSCORE players [50 100 WITHSCORES

B. ZRANGEBYSCORE players 50 100 WITHSCORES

C. ZRANGEBYSCORE players (50 (100 WITHSCORES

D. ZRANGEBYSCORE players (50 100 WITHSCORES

Solution

1. Step 1: Understand score range requirements

   Scores must be greater than 50 (exclusive) and less than or equal to 100 (inclusive).

2. Step 2: Use parentheses for exclusive and plain number for inclusive

   In Redis, (50 means greater than 50 (exclusive), and 100 means less than or equal to 100 (inclusive).

3. Step 3: Check command syntax

   ZRANGEBYSCORE players (50 100 WITHSCORES correctly uses (50 and 100 with WITHSCORES option.

4. Final Answer:

   ZRANGEBYSCORE players (50 100 WITHSCORES -> Option D

5. Quick Check:

   Exclusive lower bound uses (number) syntax [OK]

Hint: Use (number for exclusive, number for inclusive in range [OK]

Common Mistakes:

• Using brackets [] which Redis does not support for range
• Not using parentheses for exclusive bounds
• Confusing inclusive and exclusive range syntax